You got screwed up man. THERE IS NO OPTION TO TRANSFER MONEY BETWEEN USERs WALLETS. You can only trade items. Eventually sell them for wallet money at market place which you can find in Community > Market (and not directly between users).

Report this to customer support as a scam, but Valve will not give you your items back.

Yeah you got scammed. Steamrep and these sites are worthless.It's quite possible he was impersonating someone on that site too.

If you trade in steam you can swap some game items, swap games you've bought as gifts or sell a few selected things for steam wallet cash on the new market - which is quite a reasonable way of getting a bit of pocket money to spend on games, but the limitations in place suggest no one is going to retire doing it.

Other ways of exchanging items or selling them are rife with scammers, unsupported and not really a good idea.

There's very little risk if you stick with the features steam has (except for making sure you get good value for your trades, but sites like backpack.tf can help there)

None of this goes via the chat window either. If you see anything in the chat window that looks official, it was likely just typed by the buffoon on the other end, and not true.

I don't know what, if anything, steam support will do, but if nothing else just learn from the experience. If it sounded too good to be true, it probably was.

If you want to make money from Valve's games, learn how to create some good content. If something you create gets added to the game, Valve won't scam you.